Drugmaker donations to charities assisting prostate-cancer patients have dropped in wake of federal investigation, leading drug sales to fall

U.S. sales of blockbuster prostate-cancer drugs have dropped sharply since the start of a federal investigation into charities that help patients pay for these drugs, as the manufacturers have reduced donations to the charities and instead given away the medicines for free.

Drugmakers donate hundreds of millions of dollars a year to charities that help U.S. patients cover out-of-pocket costs for drugs. In turn, the drugmakers rely on the charities to effectively boost the sales of those drugs. The assistance ensures patients...